The present invention relates generally to a method and apparatus for controlling the attitude of an implement drawn by an agricultural tractor, and more spectifically to improved method and apparatus for such purpose that do not rely on measurement of the working resistances of the implement.
Many agricultural tractors are equipped with devices for automatically controlling the attitude of the implement by detecting the force exerted on the lift attachment arms, so as to optimise tractor performance by lifting the implement as a function of its working resistance. In particular, devices applied to a hydraulic lift are known in which ground action on the implement is determined by two sensors fitted to two pins about which the bottom lift arms pivot with respect to the tractor frame; and the implement is lifted by two top arms pivoting with respect to the frame, powered by a hydraulic system, and also connected mechanically to the bottom arms. In other words, the two top arms and respective bottom arms and connecting rods together define the lift. The sensors on the bottom arm pins provide for measuring deflection of the pins under the load exerted by the implement. Such a device is described, for example, in European patent application no. 95203063.3 (in the name of New Holland Italia S.p.A.) in which the agricultural tractor described employs two Hall-effect deflection sensors located at the attachment points of the lift arms to the frame.
The neutral plane of the sensors remains substantially perpendicular at all times to the ground being worked, so that the apparatus shown in the European application identified above, and similar apparatus, do not allow for the deflection sensor being rotated a given angle with respect to the ground. For this reason, since the deflection sensor detects stress substantially perpendicular to the neutral plane, the arrangement shown in the above-identified European application only provides for measuring the pulling force of the implement, which results in poor measurement and control when the pulling force is affected by the configuration as opposed to the working depth of the implement.
With an implement such as a ripper, in which the pulling force is mainly exerted by the ends, and which provides for producing drainage holes of more or less constant depth, on encountering ground areas of different consistency, pull-controlled lifting is only effective in the presence of considerable undesired variations in working depth. Lifting also produces an increase in vertical load due to the geometry of the ends, which results in increased lift pressure in the hydraulic circuit and in a chain reaction which may even result in the implement being withdrawn completely from the ground. At which point, the system commands a rapid downstroke, thus resulting in jerky operation with the implement being continually withdrawn and lowered rapidly.
Accordingly, it is an object of the present invention to provide novel and improved method and apparatus for controlling the attitude of an implement drawn by an agricultural tractor, and which enables the operator to selectively adjust the tilt of the deflection sensors with respect to the ground plane. More particularly, these novel method and apparatus provide for tilting the neutral plane of the sensor with respect to the substantially horizontal ground plane for different working conditions of the implement and different ground consistencies and properties.
Another object of the invention is to provide method and apparatus wherein the deflection sensor detects not only the pulling force of the implement but also a sustaining and lifting force component indicating, instant by instant, the way in which the pulling force is actually affected by the lifting force. The lifting force produces a component on the read axis of the sensor but oppositely oriented with respect to the pulling force projection, so that the electronic central control unit receives a lower reading which slows down, and eventually arrests, the lift operation in proportion to the ground penetration force of the implement. The lift operation can therefore be arrested long before the implement is withdrawn completely from the ground, thus eliminating any jerkiness and enabling smooth operation more in keeping with conditions external to the automatic implement lift system.
These and other objects, features and advantages are accomplished according to the instant invention by providing method and apparatus for controlling the attitude of an implement drawn by an agricultural tractor, the device comprising a lift; two deflection sensors located at the attachment points of the bottom arms of the lift to the frame of the agricultural tractor; and an electronic central control unit for processing data received from the sensors and controlling lifting and lowering of the implement by the lift as a function of the data detected by the two sensors. The device is further characterised in that each of the sensors comprises locking means for adjusting the position of the sensor with respect to the frame so that the sensor assumes a predetermined tilt with respect to the ground.